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Geoscience and Remote Sensing, IEEE Transactions on

Issue 4  Part 1 • Date July 2000

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Displaying Results 1 - 25 of 25
  • Inverse scattering problems with multifrequency data: reconstruction capabilities and solution strategies

    Publication Year: 2000 , Page(s): 1749 - 1756
    Cited by:  Papers (35)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (329 KB)  

    The aim of this paper is twofold. First, why and how exploitation of multifrequency information is of great usefulness in inverse scattering problems is discussed. Second, three different solution strategies, all based on a recently introduced approach, are presented, discussed, and compared in the actual case of noise affected data in the two-dimensional (2D) scalar case. The first one is a (nonlinear) frequency-hopping technique, which favorably compares with approaches of the same kind that use linear inversion steps. As a second approach, the contemporary use of the different frequencies data is considered. Contrary to common assumptions, it is shown that such an approach may perform better than the previous one, the different performances between the two being dictated by the spatial frequency content of the unknown contrast. Finally, a hybrid and, to the best of the authors' knowledge, novel strategy, which exploits the advantages of the the previous ones, is introduced and discussed. View full abstract»

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  • Three-dimensional finite-difference resistivity modeling using an upgridding method

    Publication Year: 2000 , Page(s): 1544 - 1550
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (164 KB)  

    The finite-difference method (FDM) for solving three-dimensional (3-D) resistivity problems has traditionally used a graded, rectangular grid whose spacings change independently in orthogonal coordinate axis directions. Small cell sizes are used to represent the field around external sources or fine resistivity features. The cell sizes are increased gradually toward the boundaries of a computational domain. Typically, cells can have very large aspect ratios, especially near the computational domain boundaries. Large round-off errors and slow convergence of (iterative) numerical solutions to the finite-difference (FD) equation system may result. In this paper, we present an upgridding approach to improve the efficiency of the FDM with a conventional rectangular grid. The upgridding process coalesces cells of extremal shapes in the directions of short dimensions to reduce cell aspect ratios and the total number of unknowns. Our experiments with a set of 3-D resistivity models show that the upgridding FDM can reduce the computation time by nearly half relative to using the FDM with a graded, rectangular grid View full abstract»

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  • Conductive masses in a half-space Earth in the diffusive regime: fast hybrid modeling of a low-contrast ellipsoid

    Publication Year: 2000 , Page(s): 1585 - 1599
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB)  

    Electromagnetic three-component magnetic probes at diffusion frequencies are now available for use in slim mineral-exploration boreholes. When a source is operated at or below the surface of the Earth in the vicinity of a conductive orebody, these probes provide, after appropriate processing, the secondary vector magnetic field attributed to this body. Proper inversion of the resulting datasets requires as a first step a clear understanding of the electromagnetic interaction of model signals with model bodies. In this paper, the response of a conductive ellipsoid buried at shallow depth in a half-space Earth is investigate by a novel hybrid approach combining the localized nonlinear approximation and the low frequency scattering theory. The ellipsoidal shape indeed fits a large class of scatterers and yet is amenable to analytical calculations in the intricate world of ellipsoidal harmonics, while the localized nonlinear approximation is known to provide fairly accurate results at least for low contrasts of conductivity between a scattering body and its host medium. In addition, weak coupling of the body to the interface is assumed. The primary field accounts for the presence of the interface, but multiple reflection of the secondary field on this interface is neglected. After analyzing the theoretical bases of the approach, numerical simulations in several geometrical and electrical configurations illustrate how estimators of the secondary magnetic field along a nearby borehole behave with respect to a general-purpose method-of-moments (MoM) code. Perspectives of the investigation and extensions, in particular, to two-body systems, strong coupling to the interface, and high contrast cases, are discussed View full abstract»

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  • Super-resolution of coherent targets by a directional borehole radar

    Publication Year: 2000 , Page(s): 1725 - 1732
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (172 KB)  

    An analytical method based on the multiple signal classification (MUSIC) algorithm is applied to three-dimensional (3D) estimation of target positions using a directional borehole radar. A cylindrical conformal array on a conducting cylinder in a borehole was used for experimental measurements estimating the position of targets. It is also shown that the algorithm provides much better resolution than the Fourier-based algorithm in both a computer simulation and real tests. Soil at the experimental site is not necessarily uniform, and there can be many clutter sources such as small stones in the subsurface. For this situation, it is difficult for the super-resolution technique to work properly. Results of the experiments show that the super-resolution technique for locating targets, despite being seriously limited by both the space available for the array and the bandwidth, is promising for directional borehole radar. In the developed algorithm, it is assumed that the distribution of electromagnetic constants inside a borehole is known before estimation of target positions View full abstract»

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  • Three-dimensional inverse scattering applied to cross-well induction sensors

    Publication Year: 2000 , Page(s): 1669 - 1681
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    Cross-well induction logging as known in the oil industry is a method for determining the electrical conductivity distribution between boreholes from the low-frequency electromagnetic field measurements in the boreholes. The authors discuss the reconstructions of the three-dimensional (3D) conductivity distribution using the contrast source inversion (CSI) method. In order to improve the reconstruction results, the concept of the extended Born approximation has been used to arrive at a preconditioning operator. Results of a number of numerical examples show that by using this preconditioning operator, a large conductivity contrast of the unknown objects (factor of 100) can be reconstructed up to an acceptable degree of accuracy. Moreover, in each iteration, the computational effort to generate the preconditioning operator is negligible View full abstract»

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  • A frequency-aspect extrapolation algorithm for ISAR image simulation based on two-dimensional ESPRIT

    Publication Year: 2000 , Page(s): 1743 - 1748
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB)  

    A frequency-aspect extrapolation algorithm is proposed to accelerate ISAR image simulation using fast multipole solvers. A two-dimensional (2D) multiple-arrival model based on high-frequency physics is proposed to parameterize the induced currents on the target. A 2D estimation of parameters via rotation invariance technique (ESPRIT) algorithm is developed to estimate the model parameters from a limited number of computed data samples in frequency and aspect. The model is then extrapolated to other frequencies and aspects to arrive at broadband, wide-angle radar cross section (RCS) data for inverse synthetic aperture radar (ISAR) image construction. This algorithm is tested using a canonical cylinder-plate structure to evaluate its performance. The ISAR image of the benchmark VFY-218 airplane at UHF band is then predicted using the fast multipole solver FISC and the 2D extrapolation algorithm. The resulting image compares favorably with that obtained from chamber measurement data View full abstract»

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  • Scattering from dielectric random fractal surfaces via method of moments

    Publication Year: 2000 , Page(s): 1644 - 1655
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB)  

    This paper presents the rationale for the use of method of moments (MoM) for evaluation of electromagnetic field scattered by dielectric random fractal surfaces. Derivation of the algorithm is given along with a reliable fractal profile generation procedure. Numerical results are compared and validated against those obtained under the hypotheses of the small perturbation scattering theory, available together with the applicability limits in the current literature. Choice of key parameters pertinent to MoM is also discussed. Numerical results are finally used to investigate the behavior of the electromagnetic scattering from fractal surfaces View full abstract»

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  • Integral equation formulation for iterative calculation of scattering from lossy rough surfaces

    Publication Year: 2000 , Page(s): 1609 - 1615
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (120 KB)  

    The dependence of the convergence properties of iterative solution algorithms on the specific integral equation formulation that is discretized to describe the electromagnetic scattering from one-dimensional (1-D) rough, high loss surfaces is examined. A magnetic field integral equation (MFIE) formulated using impedance boundary conditions typically used to describe vertically polarized (VV) scattering from large-conductivity, single-valued open surfaces yields well-conditioned interaction matrices that lead to quick convergence. The corresponding electric field integral equation (EFIE) typically used for horizontal polarization (HH) (found from duality) results in much poorer conditioning, with correspondingly slower convergence. An impedance-boundary condition magnetic field integral equation (MFIE) valid at horizontal polarization is formulated that leads to convergence nearly as rapid that observed with the vertical polarization MFIE. Numerical integration of some off-diagonal terms is required to prevent a strong singularity in the HH MFIE from introducing errors in the calculated far-field scattering. A simple example also shows that the EFIE and MFIE for the same polarization can be linearly combined to improve the convergence characteristics with lossy closed-body problems, analogous to the combined field integral equation (CFIE) perfectly conducting case View full abstract»

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  • A Volterra series approach to nonlinear traveltime tomography

    Publication Year: 2000 , Page(s): 1733 - 1742
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (196 KB)  

    Nonlinear tomographic reconstruction algorithms are developed for inversion of traveltime measurements in scattering experiments in which data models are derived from an arbitrarily large (possibly infinite) number of terms in the perturbation solution to the ray or eikonal equations. The algorithms attain the form of a Volterra series of nonlinear operators, with the usual linear reconstruction algorithm of traveltime tomography as the leading term. A computer simulation study is included to illustrate the performance of the algorithms for the case of scattering objects with cylindrical symmetry View full abstract»

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  • A new shape-based method for object localization and characterization from scattered field data

    Publication Year: 2000 , Page(s): 1682 - 1696
    Cited by:  Papers (33)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    The problem of characterizing the geometric structure of an object buried in an inhomogeneous halfspace of unknown composition is considered. The authors develop a nonlinear inverse scattering algorithm based on a low-dimensional parameterization of the unknown object and the background. In particular, they use a low-order polynomial expansion to represent the spatial variations in the real and imaginary parts of the object and background complex permittivities. The boundary separating the target from the unknown background is described using a periodic, quadratic B-spline curve whose control points can be individually manipulated. They determine the unknown control point locations and contrast expansion coefficients using a greedy-type approach to minimize a regularized least-squares cost function. The regularizer used here is designed to constrain the geometric structure of the boundary of the object and is closely related to snake methods employed in the image processing community. They demonstrate the performance of their approach via extensive numerical simulation involving two-dimensional (2D), TMz scattering geometries. Their results indicate a strong ability to localize and estimate the shape of the object even in the presence of an unknown and inhomogeneous background View full abstract»

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  • Applications of nonuniform fast transform algorithms in numerical solutions of differential and integral equations

    Publication Year: 2000 , Page(s): 1551 - 1560
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    We review our efforts to apply the nonuniform fast Fourier transform (NUFFT) and related fast transform algorithms to numerical solutions of Maxwell's equations in the time and frequency domains. The NUFFT is a fast algorithm to perform the discrete Fourier transform of data sampled nonuniformly (NUDFT). Through oversampling and fast interpolation, the forward and inverse NUFFTs can be achieved with O(N log2 N) arithmetic operations, asymptotically the same as the regular fast Fourier transform (FFT) algorithms. Using the NUFFT scheme, we develop nonuniform fast cosine transform (NUFCT) and fast Hankel transform (NUFHT) algorithms. These algorithms provide an efficient tool for numerical differentiation and integration, the key in the solutions to differential equations and volume integral equations. We present sample applications of these nonuniform fast transform algorithms in the numerical solution to Maxwell's equations View full abstract»

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  • Time statistics of propagation over the ocean surface: a numerical study

    Publication Year: 2000 , Page(s): 1626 - 1634
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB)  

    Temporal evolution of the ocean surface affects the received signal characteristics in a shipboard communication system. Predicting these time-varying properties is important in studying multipath fading problems. A statistical channel description to the second order is provided by knowledge of the coherent and incoherent power levels as well as the power spectrum of the received field. Several other time-dependent properties of a Gaussian channel can be determined from these statistics. In this paper, a method of moments (MoM) model for propagation over a one-dimensional (1D) time-evolving, perfectly conducting rough surface is applied to numerically study time statistics of propagation over the ocean. The ocean surface is described by a Pierson-Moskowitz spectrum and evolves in time according to a linear hydrodynamic dispersion relation. Due to the large size of propagation geometries in terms of the electromagnetic wavelength, an efficient numerical method is required to complete the simulation in a reasonable time. The recently developed forward-backward method with a novel spectral acceleration (F-B/NSA) technique is applied and enables time-evolving simulations for many realizations to be calculated so that reasonable statistics are obtained. Numerically obtained results for the coherent and the incoherent powers are illustrated. These results are compared with available analytical approximations to investigate the success of the approximate methods. Particular emphasis is placed on comparison with the Kirchhoff approximation, which provides reasonable predictions for smoother surface profiles and larger grazing angles View full abstract»

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  • Numerical simulations of scattering from time-varying, randomly rough surfaces

    Publication Year: 2000 , Page(s): 1616 - 1625
    Cited by:  Papers (57)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB)  

    The literature has seen the development of robust and efficient numerical techniques for exact calculations of rough surface scattering. We discuss how such methods, typically formulated for time-independent surfaces, can be extended to calculate scattering from time-evolving ocean-like surfaces. Estimates are provided for the choice of parameters in such time-varying simulations. The method of ordered multiple interactions (MOMI) is used to calculate time-varying scattering from surfaces generated according to linear and nonlinear (Creamer) models for incidence angles ranging from normal to low grazing. We discuss the runtime considerations and demonstrate that combining the MOMI with a fast multipole method (FMM)-type acceleration technique makes large-scale time-varying Monte Carlo simulations possible. The average Doppler spectra of backscattered signals obtained from such simulations are compared for different incident angles, polarizations, and surface models. In particular, the simulations show a broadening of the Doppler spectra for nonlinear surfaces, especially at low grazing angles (LGA) and a separation of the vertical and horizontal polarization spectra at LGA for nonlinear surfaces. This spectral separation at LGA is not observed when the linear surfaces are used View full abstract»

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  • Finite-difference computation of transient electromagnetic waves for cylindrical geometries in complex media

    Publication Year: 2000 , Page(s): 1530 - 1543
    Cited by:  Papers (40)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    We present two novel, fully three-dimensional (3-D) finite-difference time-domain (FDTD) schemes in cylindrical coordinates for transient simulation of electromagnetic wave propagation in complex (inhomogeneous, dispersive, and conductive) and unbounded media. The proposed FDTD schemes incorporate an extension of the perfectly matched layer (PML) absorbing boundary condition (ABC) to three-dimensional (3-D) cylindrical coordinates. Dispersion on the media is modeled by using the piecewise-linear recursive convolution (PLRC) algorithm, accounting for multiterm Lorentz and/or Debye models. Split-field and unsplit (anisotropic medium) formulations of the cylindrical PML-PLRC-FDTD schemes are implemented and compared in the time domain. The comparison includes the late-time stability properties of the update schemes. Numerical simulations of subsurface electromagnetic problems are included. Because the proposed schemes retain the nearest-neighbor property of the ordinary FDTD, they are well suited for implementation on massively parallel computers View full abstract»

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  • Parallel implementation of the sparse-matrix/canonical grid method for the analysis of two-dimensional random rough surfaces (three-dimensional scattering problem) on a Beowulf system

    Publication Year: 2000 , Page(s): 1600 - 1608
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (188 KB)  

    Wave scattering from two-dimensional (2-D) random rough surfaces [three-dimensional (3-D) scattering problem] has been previously analyzed using the sparse-matrix/canonical grid (SM/CG) method. The computational complexity and memory requirement of the SM/CG method are O(N log N) per iteration and O(N), respectively, where N is the number of surface unknowns. Furthermore, the SM/CG method is FFT based, which facilitates the implementation on parallel processors. In this paper, we present a cost-effective solution by implementing the SM/CG method on a Beowulf system consisting of PCs (processors) connected by a 100 Base TX Ethernet switch. The workloads of computing the sparse-matrix-vector multiplication corresponding to the near interactions and the fast Fourier transform (FFT) operations corresponding to the far interactions in the SM/CG method can be easily distributed among all the processors. Both perfectly conducting and lossy dielectric surfaces of Gaussian spectrum and ocean spectrum are analyzed thereafter. When possible, speedup factors against a single processor are given. It is shown that the SM/CG method for a single realization of rough surface scattering can be efficiently adapted for parallel implementation. The largest number of surface unknowns solved in this paper is over 1.5 million. On the other hand, a problem of 131072 surface unknowns for a PEC random rough surface of 1024 square wavelengths only requires a CPU time of less than 20 min. We demonstrate that analysis of a large-scale 2-D random rough surface feasible for a single realization and for one incident angle is possible using the low-cost Beowulf system View full abstract»

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  • Multifrequency dielectric profile inversion for a cylindrically stratified medium

    Publication Year: 2000 , Page(s): 1716 - 1724
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB)  

    The linear and the quadratic Born approximations of the inverse scattering problem are analyzed in the case of multifrequency measurements. The attention is focused on the determination of the maximum number of independent data available to perform the inversion for a fixed frequency interval. This number is obtained by performing the Fourier transform of the field scattered by the object under test and calculating its bandwidth under both the approximations. The results were that the quadratic model allows the authors to achieve a double number of independent data, changing the class of profiles that can be reconstructed with respect to the linear model. In order to show the validity of this conclusion, a numerical example of inversion under the two different models is performed View full abstract»

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  • A novel acceleration algorithm for the computation of scattering from two-dimensional large-scale perfectly conducting random rough surfaces with the forward-backward method

    Publication Year: 2000 , Page(s): 1656 - 1668
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (436 KB)  

    The forward-backward method with a novel spectral acceleration algorithm (FB/NSA) has been shown to be an extremely efficient iterative method of moments (MoM) for the computation of scattering from one-dimensional (1D) perfect electric conducting (PEC) and impedance rough surfaces. The NSA algorithm is employed to rapidly compute interactions between widely separated points in the conventional FB method and is based on a spectral domain representation of source currents and the associated Green's function. For fixed surface roughness statistics, the computational cost and memory storage of the FB/NSA method are 𝒪(Ntot) as the surface size increases, where Ntot is the total number of unknowns to be solved. This makes studies of scattering from large surfaces, required in low grazing-angle scattering problems, tractable. In this paper, the FB/NSA method is extended to analyze scattering from two-dimensional (2D) rough surfaces. The NSA algorithm for this case involves a double spectral integral representation of source currents and the 3D free-space scalar Green's function. The coupling between two spectral variables makes the problem more challenging, and the efficiency improvements obtained for 2D surfaces are appreciable but not as dramatic as those for 1D surfaces. However, the computational efficiency of the FB/NSA method for 2D rough surfaces remains 𝒪(Ntot) as one of the surface dimensions increases. Comparisons of numerical results between the conventional FB method and the FB/NSA method for large-scale PEC rough surfaces show that the latter yields identical results to the former with a reduction of CPU time and only a slight increase in memory storage View full abstract»

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  • Three-dimensional FDTD modeling of a ground-penetrating radar

    Publication Year: 2000 , Page(s): 1513 - 1521
    Cited by:  Papers (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (332 KB)  

    The finite-difference time-domain (FDTD) method is used to simulate three-dimensional (3-D) geometries of realistic ground-penetrating radar (GPR) scenarios. The radar unit is modeled with two transmitters and a receiver in order to cancel the direct signals emitted by the two transmitters at the receiver. The transmitting and receiving antennas are allowed to have arbitrary polarizations. Single or multiple dielectric and conducting buried targets are simulated. The buried objects are modeled as rectangular prisms and cylindrical disk. Perfectly-matched layer absorbing boundary conditions are adapted and used to terminate the FDTD computational domain, which contains a layered medium due to the ground-air interface View full abstract»

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  • A finite-difference model to study the elastic-wave interactions with buried land mines

    Publication Year: 2000 , Page(s): 1505 - 1512
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB)  

    A two-dimensional (2-D) finite-difference model for elastic waves in the ground has been developed. The model uses the equation of motion and the stress-strain relation, from which a first-order stress-velocity formulation is obtained. The resulting system of equations is discretized using centered finite-differences. A perfectly matched layer surrounds the discretized solution space and absorbs the outward traveling waves. The numerical model is validated by comparison to an analytical solution. The numerical model is used to study the interaction of elastic waves with a buried land mine. It is seen that the presence of an air-chamber within the mine gives rise to resonant oscillations that are clearly visible on the surface above the mine. The resonance is shown to be due to flexural waves being trapped within the thin layer between the surface of the ground and the air chamber of the mine. The numerical results are in good qualitative agreement with experimental observations View full abstract»

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  • Multilevel fast-multipole algorithm for scattering from conducting targets above or embedded in a lossy half space

    Publication Year: 2000 , Page(s): 1561 - 1573
    Cited by:  Papers (62)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (432 KB)  

    An extension of the multilevel fast multipole algorithm (MLFMA), originally developed for targets in free space, is presented for the electromagnetic scattering from arbitrarily shaped three-dimensional (3-D), electrically large, perfectly conducting targets above or embedded within a lossy half space. We have developed and implemented electric-field, magnetic-field, and combined-field integral equations for this purpose. The nearby terms in the MLFMA framework are evaluated by using the rigorous half-space dyadic Green's function, computed via the method of complex images. Non-nearby (far) MLFMA interactions, handled efficiently within the multilevel clustering construct, employ an approximate dyadic Green's function. This is expressed in terms of a direct-radiation term plus a single real image (representing the asymptotic far-field Green's function), with the image amplitude characterized by the polarization-dependent Fresnel reflection coefficient. Examples are presented to validate the code through comparison with a rigorous method-of-moments (MoM) solution. Finally, results are presented for scattering from a model unexploded ordnance (UXO) embedded in soil and for a realistic 3-D vehicle over soil View full abstract»

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  • Application of physics-based two-grid method and sparse matrix canonical grid method for numerical simulations of emissivities of soils with rough surfaces at microwave frequencies

    Publication Year: 2000 , Page(s): 1635 - 1643
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    The simulations of emissivities from a two-dimensional (2D) wet soil with random rough surfaces are studied with numerical solutions of three-dimensional (3D) Maxwell equations. The wet soils have large permittivity. For media with large permittivities, the surface fields can have large spatial variations on the surface. Thus, a dense discretization of the surface is required to implement the method of moment (MoM) for the surface integral equations. Such a dense discretization is also required to ensure that the emissivity can be calculated to the required accuracy of 0.01 for passive remote sensing applications. It has been shown that the physics-based two-grid method (PBTG) can efficiently compute the accurate surface fields on the dense grid. In this paper, the numerical results are calculated by using the PBTG in conjunction with the sparse-matrix canonical grid method (SMCG). The emissivities are illustrated for random rough surfaces with Gaussian spectrum for different soil moisture conditions. The results are calculated for L- and C-bands using the same physical roughness parameters. The numerical solutions of Maxwell's equations are also compared with the popular H and Q empirical model View full abstract»

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  • Variational Born iteration method and its applications to hybrid inversion

    Publication Year: 2000 , Page(s): 1709 - 1715
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    A new iteration method for electromagnetic inverse scattering is presented. This method, called the variational Born iteration method (VBIM), shows its efficiency much better than the distorted Born iteration method. VBIM has also been used for hybrid iteration inversion. Moreover, the analytic characteristics of the numerical mode match (NMM) solution were used in the inversion integral equation to speed up the calculation. Some procedures to gain the stability of the inverse solution are also discussed View full abstract»

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  • A computational technique based on a real-coded genetic algorithm for microwave imaging purposes

    Publication Year: 2000 , Page(s): 1697 - 1708
    Cited by:  Papers (74)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    A computational approach based on a genetic algorithm is proposed for the solution of a nonlinear inverse scattering problem for short-range microwave imaging applications. Starting from an integral-equation formulation, the aim is to derive locations, shapes, and distributions of the dielectric parameters of cylindrical scatterers. Simultaneously, the approach also provides the distributions of the internal total electric field. After discretization, the problem is recast as a nonlinear optimization problem. The paper exploits the application of a real-coded genetic algorithm in order to minimize a suitable functional. The reconstruction of strong scatterers with a resolution beyond the Rayleigh criterion is shown, and computational aspects are discussed. Comparisons with results obtained by using approximated formulations and a binary-coded genetic algorithm are also provided. Finally, a hybrid version of the approach (based on the combined strategy of the genetic algorithm and a conjugate gradient method) is presented and preliminarily tested View full abstract»

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  • A three-dimensional transmission line matrix method (TLM) for simulations of logging tools

    Publication Year: 2000 , Page(s): 1522 - 1529
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB)  

    A three-dimensional (3-D) transmission line matrix method (TLM) in cylindrical coordinates for the simulation of logging tools is formulated and programmed. The radiation properties of a coil-type antenna in a conductive medium are analyzed and simulated with TLM formulations. The symmetrical condensed nodes (SCN) are adopted. This algorithm can be applied to both induction and measuring-while-drilling (MWD) tools in both the time and frequency domains, and the formation can be anisotropic. Perfectly matched layer (PML) absorbing boundary conditions are used to simulate an infinite boundary in real logging situations. Verifications and some examples are presented View full abstract»

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  • Modeling of radiowave scattering in the melting layer of precipitation

    Publication Year: 2000 , Page(s): 1574 - 1584
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB)  

    In this paper, a new melting layer model called melting layer with spheroidal particles (CFPS in French) is presented. The physical description of the melting layer and the method of scattering calculation used in this model are developed. Two important contributions are the nonmonotonous law for the axial ratio of melting particles and the scattering calculation, which is made by an exact method for a spheroidal particle with any size and any axial ratio. The CFPS model is validated with radar data at 3 and 35 GHz. Results of validation are shown in this paper. Two applications are discussed: the comparison between three other melting layer models (developed by the European Space Agency, Delft University, and Helsinki University) that run faster in time but involve limitations in particle size or particle shape and a radar data inversion process in order to better characterize the melting layer and to retrieve meteorological parameters View full abstract»

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Aims & Scope

 

IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING (TGRS) is a monthly publication that focuses on the theory, concepts, and techniques of science and engineering as applied to sensing the land, oceans, atmosphere, and space; and the processing, interpretation, and dissemination of this information.

 

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Antonio J. Plaza
University of Extremadura